Childhood Obesity Linked to Increased Risk of Adult Childlessness

Tracking Childhood Weight Trajectories in Denmark

Researchers examined health records from the Copenhagen School Health Records Register to understand how early-life body mass index influences reproductive capacity later in life. The dataset included nearly every girl attending school in Copenhagen born between 1950 and 1989. These participants had their height and weight measured during yearly school health examinations between the ages of 6 and 15 years.

To capture distinct growth patterns, the analysis grouped the 60,864 qualifying women into five unique childhood BMI trajectories. The cohort broke down into 13,460 girls in the below-average group, 22,608 in the average group, 15,431 in the above-average group, 7,060 in the overweight group, and 2,305 in the obesity group. Investigators then linked these childhood records with the Danish Medical Birth Register covering the years from 1977 to 2022 to track who subsequently gave birth between the ages of 18 and 45.

Birth Rates and Age-Specific Disparities

Across the multi-decade study period, 78% of the women—amounting to 47,669 individuals—gave birth at an average age of 27 years, while 22% remained childless. When evaluating western European demographics more broadly, about 20% of women born around 1965 remain childless, and birth rates frequently fall below replacement levels. However, estimates suggest that only about 5% of European women aged 18 to 40 do not intend to have children, implying that the vast majority of childlessness is involuntary.

After researchers adjusted for influential factors such as birth cohort and parental educational level, clear reproductive differences emerged. Women who maintained an overweight or obesity trajectory during childhood showed a lower likelihood of giving birth compared to peers with average growth patterns.

• Between the ages of 25 and 29, women with a childhood obesity trajectory were 22% less likely to give birth than those with an average BMI trajectory.
• At ages 30 to 34, the same obesity group experienced a 42% lower likelihood of giving birth.
• Women with a childhood overweight trajectory were 9% less likely to give birth between ages 25 and 29, and 26% less likely between ages 30 and 34.

Physiological and Social Pathways to Infertility

The study highlights how reproductive health can be shaped by events occurring long before family planning begins. Lead author Dr. Dorthe C. Pedersen pointed out that while advancing age and postponed parenthood drive many cases of childlessness, excess weight introduces additional physiological and social hurdles.

“Although advancing age is a major driver of childlessness, with postponed parenthood being a substantial contributor, overweight and obesity appear to further increase these risks through physiological and social pathways, possibly including effects on egg quality and hormonal disturbances. So it is concerning that one in three school-aged girls in Europe are currently living with overweight or obesity.”

Dr. Dorthe C. Pedersen, Copenhagen University Hospital – Bispebjerg and Frederiksberg

Senior author Dr. Jennifer Baker emphasized that infertility should be viewed as a cumulative physical and social experience.